The two dollar coin denomination (written as $2) was introduced in Australia in 1988, replacing the earlier banknotes. The original reverse design by Horst Hahne on circulating coins has not been changed since its introduction. The denomination is also often used to issue circulating commemorative coins with various reverses.
Apart from the circulating coinage, both the Royal Australian Mint and the Perth Mint have extensive programs issuing $2 coins for collectors (Non-Circulating Legal Tender, or NCLT), such as this one.
This coin was issued as part of the 1999 Masterpieces in Silver - Coins of the 20th Century: Memories six-coin set, highlighting important times in Australian history (mintage limit 15,000, issue price A$125.00). The reverses of each coin show a historic Australian coin design, in mirror-finish proof; the denomination and value are on the obverse.
The five cents coin depicts a 1939 kangaroo-type halfpenny.
The ten cents coin depicts a 1930 penny.
The twenty cents coin depicts a 1942 threepence.
The fifty cents coin depicts a 1918 sixpence.
The one dollar shows a 1940 shilling.
The two dollar coin shows a 1920 sovereign with an S mint mark.
In 1920, only the Australian branches of the Royal Mint were still striking imperial sovereign coins. Only 360,000 sovereigns were produced by the Sydney Mint, which closed soon after; most coins were later melted and just a handful are known to exist today.
These coins are Non-Circulating Legal Tender (collector issue); composition: fine silver (99.9%). No coins of this type have been released into circulation.